Testosterone should generally not be prescribed for men with prostate cancer (with possible exceptions in carefully selected men such as those with a history of treated low-risk, Gleason <3 + 4 prostate cancer, undetectable PSA and no clinical evidence of disease after treatment) or to men at higher risk of prostate cancer (unevaluated prostate nodule, PSA >4 ng/mL), and follow-up of prostate health during testosterone treatment should be individualized (14). Here, KLK3 is linked to prostate cancer.